So they actually did it: They turned the sprawling, insane Cloud Atlas into a movie, one that actually makes the book look straightforward and uncontroversial. It just goes to show, no matter how unconventional or sprawling a book is, there's a way to adapt that sucker into a movie. Except sometimes, no.

Here are 10 science fiction books, by some of the genre's greatest authors, that we are pretty darn sure will never be made into movies. Of course, now we're just daring Hollywood to prove us wrong.

1) Friday by Robert A. Heinlein

Arguably the best of Heinlein's late novels, this is still a controversial book at best - Jo Walton at Tor.com calls it "The worst book I love." Friday Baldwin is an artificial person, genetically engineered to be super-smart and resourceful, who works as a courier, traveling around a future Earth. Along the way, she has lots and lots of sex, joins in a group marriage, and treats us to lots of philosophizing about the nature of humanity and sex and stuff. I frequently threaten to write an essay arguing that this book was adapted into the film of the same name, featuring Ice Cube and Chris Tucker - and that's probably the closest we'll ever get to a film of this book.

2) The Left Hand of Darkness by Ursula K. Le Guin

This is one of the all-time great science fiction novels - and yet, it's also exceedingly challenging. People tend to fixate on one obvious bit of strangeness - the fact that the natives of the planet Winter (or "Gethen," in their own language) are neither male nor female except when they experience brief periods of "Kemmer." But that's just one odd point in a book that's full of oddness - Gethenian politics are also incredibly complex, including what seems to be an impending war on a world that has no concept of war. The experiences of Genly Ai, a visiting envoy from the Ekumen, involve a series of misunderstandings, political upheavals and long journeys. A lot of the action depends on understanding made-up cultural concepts such as "shifgrethor." And a huge plot device in the story, the ansible, is purely a communications tool that allows for instantaneous communication with other worlds. There's almost no way to capture even a fraction of what's going on in this novel in a standard motion picture.

3) When HARLIE Was One by David Gerrold

The obvious Gerrold book to include on this list might be The Man Who Folded Himself, which is full of time-traveling orgies and general weirdness - but we've already included that on some other lists of weird books. And HARLIE Was One is actually quite weird in its own right. When I first read this book, it completely melted my brain - and I've been curious to go back and read the revised version that Gerrold put out, "Version 2.0," to see how much odder it might be. I have a strong suspicion that this loopy story about artificial intelligence probably inspired a lot of the weirdest cyberpunk stuff, including Rudy Rucker's Ware tetralogy. In a nutshell, this novel is about an artificial intelligence named HARLIE that's created by a corporation - and is a little too human for its owners' liking, including experiencing drug trips and writing weird poetry. HARLIE is pushed to prove that it can turn a profit, so it comes up with a bizarre scheme to extend its capabilities nearly to infinity, with the G.O.D. Project. Completely demented, in the best possible way - but it's hard to imagine anybody making a movie about a friendly computer that trips balls, writes poetry and wants to be God.

4) Woman on the Edge of Time by Marge Piercy

Another classic from the 1970s, that still holds a lot of power today. Piercy's novel is challenging for a few reasons, including the somewhat confusing method of time travel - a woman who's receiving electric shock therapy in a mental institution travels forward in time, apparently mentally. There's also the fact that she seems to alternate between two different futures, one utopian (in a very 1970s way) and the other dystopian. People who read this novel looking for a straightforward plot are probably going to be somewhat confounded, although its notions of dispossessed people visualizing a better future remain compelling. Even if a film of Edge of Time were considered commercial - which is rather a big "if" - it's almost impossible to imagine translating the "mental time travel" concept and dueling timelines into a form that moviegoers could make sense out of. Maybe after the utopian commune future arrives, we'll create the perfect holographic recreation of this book.

5) Glasshouse by Charles Stross

One of Stross' most challenging books, the bulk of Glasshouse takes place in a recreation of Twentieth Century Earth - which ought to be a snap to translate into movie form, right? Except that it's very important that everybody is aware that this is a simulation, and it's wrong in some subtle but important ways, because it's based on incomplete historical records. And it's also an indispensible part of the story that the main character, who's put into a woman's body, is actually a posthuman man who spent a good amount of time as a tank. And there's rather a lot of having sex with four-armed, polymorphous humanoids early on, setting up a vital contrast with the conformity and coercion that follows. Also, the story doesn't entirely work without awareness of concepts such as jumpgates that allow travel across long distances, the Censorship Wars, and the virus known as Curious Yellow. As the story progresses, it depends more and more on those sorts of strange concepts, and stripping all of that stuff away leaves something weirdly hollow, almost like a victim of the Censorship Wars.

6) The Four-Gated City by Doris Lessing

This is a strong contender for my favorite book of all time - but it's also completely bugged out. (I just realized we did include it on our previous list of weird books that are required reading. Sorry for the overlap!) There's a pretty simple reason whyFour-GatedCitywill never be a movie - it's the fifth book in Lessing's Martha Quest series, and you'd probably have to film the first four books first. The first few books in the series are completely realistic fiction, loosely based on Lessing's own experiences, but they include some fairly challenging stuff, like what it was like to be a member of the Communist party in the 1950s in Africa, and <em>actually believe Stalin was a great leader</em>. By the time you get toFour-GatedCity, it's the late 1960s, and the Sexual Revolution has hit, leading to lots of weird exploration including sleep deprivation and sitting staring at each other naked for hours without touching. Over the course of the book, tons of people start developing psychic powers and the world starts to collapse, until there's finally kind of an ambiguous apocalypse. The weirdness sneaks up on you bit by bit, until you're no longer quite sure when this book stopped being straight-up realism about the present, and moved into the future.

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7) Across Realtime by Vernor Vinge

This book (made up of three smaller works, combined by Baen in 1991) is a lot less experimental than some of the other books on this list - but it spans huge expanses of time. And its central concept, of "Bobbling," is one that might be difficult to depict on screen and hard for movie audiences to grasp. In a nutshell, Bobbles are stasis fields, that keep everything inside them completely unchanged for years. Or centuries. Or millennia. Or even longer. Each Bobble has its own preset lifespan, so that two sets of people that were Bobbled at different points in the past could emerge at the same point in the future. This power is first used by the Peace Authority to try and end warfare by imprisoning people and their weapons inside Bobbles - but soon it becomes much more than a tool of social control. As in all the best science fiction, Vinge takes a single radical concept and brings it much further than you could have expected, until by the end of the story the Bobbles have become a way of looking at the whole sweep of history. You could easily make a movie about someone inventing stasis fields that last a few days or even a year, but it's hard to imagine a story about stasis fields that can last so long and have such variable lifespans.

8) Among Others by Jo Walton

The latest Hugo and Nebula winning novel has been widely, and justly, praised for its depiction of growing up geeky and seeking solace in science fiction books. (Read our review here, and read our fascinating reader chat with Walton here. But it's almost impossible to imagine Among Others working as a movie, for the exact reasons that it works so well as a book - the blend of memoir, beguilingly strange fantasy and book criticism depends on Walton's voice, and there's almost no way to pull out the bones of the story without including all of the musings on classic 1970s novels and storytelling, and the responsible use of magical powers. The spell that Walton weaves here is made solely out of words, and can't really be translated into pure images without losing its essence.

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9) They Walked Like Men by Clifford Simak

This is another book that left a really strange impression on my mind - it's an early 1960s freakout in which a journalist discovers that aliens, who look like bowling balls but can take on human shape via "dolls," are buying our planet. Piece by piece. And then basically liquidating all of it. It's a weirdly prescient story about the downside of extreme capitalism - the aliens use their wealth to buy stores and close them, leading to an economic meltdown. The aliens also buy up all the houses and evict the people from them, forcing everybody to live in their cars. But then the aliens' cash disappears once it's deposited in the banks. Oh, and there are talking dogs, too.

10) The Sparrow by Mary Doria Russell

And finally, there's another all-time classic… that might be a little too challenging to make it to the movies, even in a massively adulterated form. Even if you could get people to deal with the notion of Jesuits traveling to another planet and making first contact with an alien species, the awful fate that befalls the main character Sandoz is almost impossible to picture appearing on the big screen. Actually, there were two attempts to make "action adventure" versions, starring Antonio Banderas and Brad Pitt respectively. Those both fell through, and Russell herself co-wrote a much more faithful screenplay with her friend Karen Hall. Unfortunately, that version of the script had no takers, even though one director was eager to take it on. This past April, Russell reported that she'd been approached by the writer of the Brad Pitt version of the screenplay, wanting to try again - and she turned him down, because she's decided that a Hollywood version of The Sparrow would inevitably eliminate almost everything that makes readers connect with her book. Added Russell,

Michael's adaptation made sense in the context of what Hollywood is likely to buy and/or produce, but it changed too much of the story for it to be satisfying to the many readers who genuinely love that novel. And I don't want to spend the rest of my life apologizing to people who would feel betrayed by a screen adaptation that didn't face up to the central issues of the story.